1. Field of the Invention
This invention relates generally to communication techniques, and more particularly to a method of exploiting the structure of pulse amplitude modulation (PAM) communication signals in order to perform interpolation at baud-rate sampling.
2. Description of the Prior Art
The timing recovery function of a digital communications receiver has to perform modifications to the sampling instants of the analog-to digital (A/D) converter. The natural solution is to modify the clock signal that controls the A/D (e.g. by using a voltage controlled oscillator). This however, is an expensive solution; and it is usually preferred that the A/D will sample with a free-running clock, and timing modifications will be done by digital interpolation of the A/D output samples. Such interpolation is practical only if the sampling rate is high enough such that a data sample can be reconstructed from several neighboring samples. Fast digital data communications standards (such as Gigabit Ethernet) however, usually use baud rate sampling (one sample per symbol), which is below the Nyquist rate of the signal, and certainly cannot be used with standard interpolation techniques.
In view of the foregoing, it is highly desirable and advantageous to provide a technique for implementing timing recovery associated with a digital communications receiver using interpolation at baud-rate sampling rates such that only a simple and inexpensive control of the A/D clock is required.